Colloidal dynamics in flow and confinement

The aim of this thesis is to understand how the diffusive dynamics and flow behaviors of colloidal hard spheres are influenced by the confinement of nearby walls. The Brownian motion of hard spheres in quiescent bulk fluids is well known, but the presence of confining walls generate new physical phenomena which are still incompletely understood. This situation applies already to the case of confinement by a single wall. In the dilute limit, the diffusion is known to slow down and become anisotropic as the wall is approached. Much less is known about the behavior in more concentrated suspensions. In this regime, hydrodynamic interactions between the particles become more important. They are modified by the structure in the fluid, which itself is also modified by the presence of the wall. Introduction of a second wall, or curved walls gives rise to further changes. All these effects are of relevance for practical problems where colloids occur inside (e.g. cylindrical) capillaries. Turning on the flow, e.g. in a micro channel, introduces additional elements. The inherent shear gradients that are set up, will increase the particle collision rate, and can change the fluid structure as well, in particular if the flow rate (i.e. Peclet number) becomes large. Locally, also direct effects of flow past a wall may occur; e.g. slip, which is related to the particle-wall interaction. The modified diffusion and flow near the wall can have significant implications for the transport of suspensions through capillaries.